OAKLAND, Calif. — There are times at this ugly concrete complex next to the freeway when you wonder why anyone would rather be anywhere else.

It happens during Raiders games when the costumed inhabitants of the Black Hole lustily cheer, or when the denizens of Section 149 in the outfield bleachers are in full throat during another October rush for the underdog A’s.

And it happens on nights like Thursday when the Warriors are raining 3-pointers from the rafters of Oracle Arena, and the opponent and the referee’s whistle are no match for the roar of 20,000 hysterical fans wearing matching yellow T-shirts.

As the faithful congregate again for Game 2 of the N.B.A. finals against the Cleveland Cavaliers on Sunday evening, you cannot help thinking: Is this mighty Oakland’s last hurrah as one of America’s great professional sports cities?

“They could lose all three teams, no question, and it would be a great blow,” said Art Spander, who has spent decades in the Bay Area writing for the likes of The San Francisco Chronicle and The San Francisco Examiner, and has lived in Oakland for about 50 years. “Oakland doesn’t have the cachet of San Francisco, or the young turks that San Jose and Silicon Valley have.”

It was not long ago that this diverse, troubled and revered port city by the bay, at turns derided and defended, considered too crime-ridden and too gentrified, was a place that sports franchises wanted to be.

When the Warriors arrived in 1971, Oakland had teams in all four major sports: the N.F.L., the N.B.A., the N.H.L. and Major League Baseball. Only six other American cities could make that boast at the time.

Now it is a place to flee. The Raiders, the A’s and the Warriors are all looking to get out, seeing greener grass beyond their concrete-and-blacktop complex.

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A view of O.co Coliseum during an A’s game last month. The team is bound to Oakland through 2018.CreditEzra Shaw/Getty Images

It is possible, if not likely, that the Oakland of 2020 will have no major teams.

The Warriors have plans to move back to San Francisco, to a glassy waterfront arena, as early as 2018. The Raiders and the A’s, trying to disconnect from each other and from the decaying stadium they share, are threatening to leave, too — the Raiders back to Los Angeles, the A’s to San Jose or anywhere else that welcomes them to a better ballpark.

Oakland was once the most successful sports city in the nation. The A’s won three consecutive World Series from 1972 to 1974. The Warriors won the N.B.A. title in 1975. The Raiders won the Super Bowl at the end of the 1976 season.

They were anchors to a city that also welcomed the Oakland Oaks (of the American Basketball Association) and the Oakland Seals (N.H.L), World Team Tennis and indoor soccer, among others.

Part of Oakland’s unique charm was — and is, for now — the geographic proximity of those teams. The Oakland-Alameda County Arena and Coliseum Complex opened in 1966. The stadium and the arena were built about 50 yards apart, connected by a small plaza, surrounded by a sea of parking places, and easily spotted from the freeway.

It has hardly changed since, a time capsule left unburied. But the landscape is shifting.

On Friday, N.B.A. Commissioner Adam Silver planned to meet with Warriors executives to discuss progress on an arena envisioned in San Francisco’s Mission Bay neighborhood, a resurgent area south of downtown and about a mile south of the Giants’ AT&T Park. It is private land, and the arena will be privately financed, the Warriors said, but ground has not been broken.

“This team needs a new arena, there is no doubt about that,” Silver said before Thursday’s game, though it was very likely that few in attendance for Golden State’s 108-100 overtime victory thought to themselves that the night would be better if only the game were somewhere else.

The proposed site is across San Francisco Bay, but about 20 miles, over the Bay Bridge, by car.

“From the league standpoint, we’ve always seen this team as the Bay Area’s team,” Silver said.

That distinguishes the Warriors from the Raiders and the A’s, cast as scruffy contrasts to their upright San Francisco counterparts, the 49ers and the Giants. The Warriors, who moved to San Francisco from Philadelphia in 1962, are a blend of those divided fan bases, unbound by geographic boundaries partly because they are the area’s only N.B.A. team.

But there are concerns that the magic happening now at Oracle can be exported. Designs for the new arena include a low ceiling to help the noise rattle, the way it does at Oracle, but something as ethereal as game-time atmosphere cannot be transferred between arenas and stadiums like carry-on luggage. Some fans of the 49ers pine for the long-lost energy of dank, windy (and now-demolished) Candlestick Park, the type of distinguishable personality yet to emerge in the polished throne of Levi’s Stadium in an office park of Santa Clara.

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Marcel Reece after a touchdown last season for the Raiders, who are eyeing the Los Angeles area as a new home.CreditThearon W. Henderson/Getty Images

The Warriors represent the rare franchise escaping an already enviable position. Co-owned by Joe Lacob and Peter Guber, who bought the franchise in 2010, the Warriors have 131 consecutive sellouts dating to December 2012. They have what is generally regarded as the N.B.A.’s best home-court advantage, measured by noise (110 decibels by one reading a couple of years ago) and standings (39-2 this last regular season).

Their popularity also made it reasonable to search for an arena that was not nearly 50 years old.

“It’s unfortunate, but that’s life in the world of sports now,” said Rick Barry, the Hall of Fame player who led the Warriors to their last N.B.A. title, after the team moved to Oakland from San Francisco. “They want to go back to where their roots are, and you can’t blame them. Where they are is antiquated.”

The Raiders and the A’s appear headed to divorce as co-inhabitants of what is now called O.co Coliseum. Each would like the other to leave, then find a way to build a one-sport stadium of its own.

The A’s have tinkered with other stadium sites, including one near the water in Oakland (a mirrored hope, perhaps, of what the Giants have across the bay), and have a persistent suitor in San Jose. But Major League Baseball says that San Jose, at the southern edge of the bay, is Giants territory, leaving the A’s stuck for now. They signed a lease extension last year that binds them in Oakland through 2018, and they have invested money in coliseum upgrades, like new video boards, to nudge the facility out of the 20th century.

Part of what makes O.co Coliseum a relatively inhospitable place to watch baseball is the wall of seats and suites that were built 20 years ago to entice the Raiders to return from Los Angeles, where the owner Al Davis took them in 1982. They block what had been a serene view of the Oakland hills beyond the outfield and eliminated the type of pavilion that so many new ballparks now relish.

The Raiders, now run by Davis’s son, Mark, could be the first of the three teams to leave Oakland — again. With no serious alternatives closer to home, the Raiders have connected with the San Diego Chargers in a stadium bid in Carson, a Los Angeles suburb. The St. Louis Rams have eyes on Los Angeles, too, at the site of the former Hollywood Park racetrack.

With momentum building to return a N.F.L. team to Los Angeles, it seems that some combination of those three franchises — one or two of them — could move there in the next couple of years. N.F.L. owners will discuss the topic at meetings in August.

“How much more disrespect can Oakland tolerate from its ungrateful three sports franchises?” Dave Newhouse, a retired longtime columnist for The Oakland Tribune, wrote recently in an essay published in Bay Area newspapers. “There isn’t another sports town anywhere that has enjoyed more success or endured more grief from its sports tenants than Oakland, the carpetbagger capital of America.”

That backdrop permeates what might be a high point in Oakland sports history. The Warriors sit three victories away from their first championship in 40 years, and from bringing Oakland its first major pro sports championship since the A’s won an earthquake-interrupted World Series in 1989.

That championship came over a team from San Francisco. Interesting if the next one — what could be the last one — is won by a team headed back there itself.

A version of this article appears in print on , on Page SP8 of the New York edition with the headline: A Home of Championship Teams, All of Them Looking to Leave . Order Reprints | Today’s Paper | Subscribe